JPH06130806A - Electrostatic-latent-image developing device - Google Patents

Abstract

PURPOSE: To provide an electrostatic latent image developing device for scavengeless developing which includes a donor roller preventing the accumulation of charge with time, having conductivity high enough to prevent the short circuit or the arc of a magnetic brush to the donor roller and having an outer surface formed of wear resistant material comparatively easily worked. CONSTITUTION: This device is equipped with a housing 38 forming a chamber for preserving replenishing developer material 47 inside; the donor roller 40 having the outer surface 42 made of phenol resin, at least partially attached to the chamber of the housing 38, and constituted to carry the material 47 to a latent image; and an electrode member 41 arranged at a proximate distance from the roller 40 in a space between the latent image and the roller 40, forming toner powder cloud in a space between the member 41 and the latent image by separating toner particles from the roller 40, and electrically biased so as to develop the latent image with the toner particles separated from the toner cloud.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for electrophotographic printing. More particularly, the present invention relates to donor rollers as part of the scavengeless development process.

[0002]

BACKGROUND OF THE INVENTION In the process of electrophotographic printing, the step of delivering toner to a latent image on a photoreceptor is known as "developing".

One important variation on the general principle of development is "scavengeles."
s) "is the concept of development. For the purpose and function of scavengeless development, see, for example, Hayes et al., US Pat.
68,600, Folkins U.S. Pat. No. 4,98
U.S. Pat. No. 5,010,367 to Hayes.
U.S. Pat. No. 5,063,87 to Forkins et al.
No. 5 for more details. Scavengeless development systems generally take the form of wires that extend across the photoreceptor and are located in the nip between the donor roller and the photoreceptor.
The toner is transported to the photoreceptor by an AC electric field provided by an aced) electrode structure. Since there is no physical contact between the developing device and the photoreceptor, scavengeless development is different, such as "tri-level" or "recharging, exposing and developing" type highlights or image stacking color xerography. It is useful in devices where different types of toner are delivered to the same photoreceptor.

[0004]

An electrostatic latent image developing device according to claim 1 is a device for developing an electrostatic latent image,
The apparatus has a housing defining a chamber for storing replenishment developer material therein, and an outer surface of a phenolic resin, the apparatus being at least partially mounted within the chamber of the housing for latent image development material. A donor roller configured to be conveyed to the donor roller, and an electrode member disposed in a space between the latent image and the donor roller at a close distance from the donor roller, wherein the toner particles are separated from the donor roller. Form a toner powder cloud in the space between the latent images,
An electrically biased electrode member for developing the latent image with toner particles separated from the toner cloud.

The electrostatic latent image developing device described in claim 2 is the device according to claim 1, wherein the discharge time constant of the surface of the donor roller is less than 300 microseconds.

An electrostatic latent image developing device according to a third aspect is the device according to the first aspect, wherein 10 ^-8 (ohm-cm) ^{-1 is used.}
It is characterized in that the phenol resin of the donor roller is doped until a conductivity of over 10 is obtained.

An electrostatic latent image developing device according to claim 4 is a device for developing an electrostatic latent image, wherein the device forms a chamber for storing replenishment developer material therein, A donor roller at least partially mounted within the chamber of the housing and configured to carry a developer material to the latent image, the discharge time constant of the surface of the donor roller being less than 300 microseconds. Characterize.

The electrostatic latent image developing device according to claim 5 is a device for developing an electrostatic latent image on a charge holding surface, wherein the device forms a chamber for storing a replenishment developer material therein. And a donor roller configured to carry a developer material to a latent image, the donor roller being at least partially mounted within a chamber of the housing and having a conductive interior and a substantially non-metallic exterior layer. And a donor roller configured such that the thickness of the outer layer divided by its dielectric constant is less than the distance between the donor roller and the charge retentive surface.

According to a sixth aspect of the present invention, there is provided an electrostatic latent image developing device according to the fifth aspect, wherein the thickness of the outer layer divided by the dielectric constant of the developer material is applied to the charge retentive surface. It is characterized by being smaller than the average diameter of the particles.

An electrostatic latent image developing device according to claim 7 is the device according to claim 5, further comprising at least one wire located in a space between the latent image and the donor roller,
An electrode member arranged at a close distance from the donor roller, separating the toner particles from the donor roller to form a toner powder cloud in the space between the donor roller and the charge holding surface, and separating the toner from the toner cloud. An electrode member that is electrically biased to develop a latent image with the particles, the outer layer thickness divided by its dielectric constant being less than the diameter of the wire.

[0011]

EXAMPLE Next, FIG. 1 will be described. This shows the development system in detail. The housing 38 forms a chamber for storing replenishment developer material 47 therein. At the bottom of the housing 38 is a horizontal auger that evenly distributes the developer material along the length of the transport roller 46 so that the bottom of the roller 46 is always in the body of the developer material. It is soaking.

The transport roller 46 is a non-magnetic material designed to rotate around the magnetic core 48 in the direction indicated by the arrow.
It comprises a stationary multi-pole magnet 48, which preferably has an aluminum sleeve 50 in close proximity. Since the developer material contains magnetic carrier particles, the developer material is attracted to the outside of the sleeve by the effect of the sleeve rotating through a stationary magnetic field. A doctor blade 62 is used to limit the radial depth of developer material remaining attached to the sleeve as it rotates to the nip 68 between the transport roller 46 and the donor roller 40. The donor roller 40 is maintained at a specific voltage by a DC power supply 76 in order to attract the thin layer of toner particles of the transport roller 46 to the surface of the donor roller 40 at the nip 68. Donor roller 40 is preferably formed on its entirety, or at least its outer layers, of a material having a low electrical conductivity, as described in detail below. This material must have sufficient conductivity to prevent charge buildup over time, and its conductivity is
It must be low enough to form a blocking layer to prevent shorting and arcing of the magnetic brush to the donor roller.

The transport roller 46 is biased by both a DC voltage source 78 and an AC voltage source 80. DC
The effect of the electric field enhances the suction of the developer material into the sleeve 50. The effect of the AC electric field occurring along the transport roller 46 at the nip 68 is believed to be the loosening of toner particle adhesion to the carrier particles and triboelectric coupling. The AC voltage power supply 80 can be applied to the transport roller 46 as shown in FIG. 1 or directly to the donor roller 40 in series with the power supply 76.

It has been found that power supply 80 outputs up to 200 Vrms are sufficient to achieve the desired level of toner particle reloading efficiency. The actual value can be adjusted empirically. Theoretically about 4
Any value up to a voltage of 00 Vrms can be taken.
The power supply should have a frequency of about 2 kHz. If the frequency is too low, for example below 200 Hz, stripes will appear on the copy. If the frequency is too high, say above 15 kHz, the system will probably work, but the electronics will be expensive due to capacitive loading losses.

An electrode wire 41 is arranged in the space between the belt 10 and the donor roller 40. A pair of electrode wires 41 are shown extending in a direction substantially parallel to the longitudinal axis of donor roller 40. The electrode wire 41 is formed of one or more thin steel wires (that is, a diameter of 50 to 100 μm) and is arranged at a position close to the donor roller 40. The distance between the wire 41 and the donor roller 40 is about 25 μm, or the thickness of the toner layer formed on the donor roller 40. The wire automatically self-spaces from the donor roller, depending on the thickness of the toner on the donor roller. To this end, the ends of the wires supported by the tops of the end bearing blocks also serve to support the donor roller for rotation. The ends of the wires are mounted slightly below the tangent to the surface containing the toner layer of the donor structure. By mounting the wire in this manner, the wire is immune to roll runout due to its self spacing. An AC electrical bias is applied to the electrode wires by an AC voltage source 84. The applied AC creates an AC electrostatic field between the wire and the donor roller, which is effective in separating toner from the surface of the donor roller and forming a toner cloud around the wire. The height of the toner cloud is a height at which the toner cloud does not substantially come into contact with the belt 10.

In the area where photoconductive belt 10 passes through the position closest to donor roller 40, stationary shoe 82 supports the inner surface of the belt. The position of the shoe relative to the donor roller determines the distance between the donor roller and the belt.
The position of the shoe is adjustable and is arranged such that the distance between the donor roller and the photoconductive belt is preferably about 0.4 mm.

Another factor that has been found to be important is the sleeve 50 relative to the rotational speed of the donor roller 40.
Is the rotation speed of. In practice, both are driven by the same motor, but because the drive system includes a gear train, sleeve 50 is driven at a faster surface speed that is more effective than donor roller 40. A transport roller to donor roller speed ratio of 3: 1 has been found to be particularly advantageous, although higher relative speeds may be used in some embodiments of the invention. Also, in another embodiment,
A speed ratio as low as 2 to 1 may be used.

FIG. 2 is a simplified plan view of a one-component scavengeless developing station. The one-component station of the particular design shown in FIG. 2 is generally disclosed in US Pat. No. 5,128,723 assigned to the assignee of the present application. 1 and 2, the same reference numerals are used for the same elements. Similar to the hybrid system of FIG. 1,
The one-component system includes a donor roller 40 and an electrode wire 4.
1, but the donor roller 40 takes toner directly from the replenishing pure toner in the housing 38 and delivers it to the photoreceptor 10. Since there is no transport roller 46 in the one component system of FIG. 2, carrier beads are not used for the developer. The particular design developer station shown in FIG. 2 may include special components useful for single component development, such as charging rod 78 and electrically biased toner mover 94. For the exact function of these parts,
It is described in said patent.

Referring to either FIG. 1 or 2, in the present invention, the outer surface 42 of the donor roller 40 is formed from a self-supporting cylinder of phenolic resin, which is preferably manufactured by Tokai Rubber Industries of Japan. Preferred are phenolic resins of the type described, especially "LGC" and "GCS '" formulations which are proprietary to this manufacturer. When using this outer roller made of phenolic resin, the core of donor roller 40 uses a conventional conductive material such as aluminum. This phenolic resin is extruded into a self-supporting tube, doped to achieve a preselected conductivity, and, if necessary, techniques well known in the art to achieve the exact dimensions required for a particular developer. Grind until worn. 1 of the present invention
In one embodiment, the wall thickness of the phenolic cylinder forming the outer surface 42 is between 1 mm and 2 mm for a donor roller 40 having a total outer diameter of about 25 mm. This thickness is a compromise between mechanical stability and cost issues. It has been revealed that the phenol resin, whether of the magnetic brush type or the one-component type, is particularly suitable for the design parameters of the donor roller for scavengeless development. Phenolic resin self-supporting tubes can be formed into relatively thick walls, so wall thickness can be used to ensure that surface anomalies such as pockmarks and pinholes are kept to a minimum. . It has been found that the phenolic resin is a moderately hard material and does not cause significant wear problems with prolonged magnetic contact with the magnetic brush. Again, since phenolic resins are relatively easy to process, it is possible to slightly polish such cylinders to ensure precise dimensions.

The main parameter of the outer surface of the donor roller according to the present invention is its discharge time constant. The discharge time constant is the amount of time that 63% of the electric charge applied to the surface of the donor roller disappears. Since these time constants are a function of the resistance and capacitance of the device, as is well known in electrical engineering, the two main parameters of a phenolic resin composition are its conductivity (which is related to resistance). ) And its dielectric constant (which is related to capacitance). The conductivity of a particular additive in a phenolic resin is a factor in its overall conductivity. Among the conductive materials that can be used to achieve the desired conductivity are weakly conductive materials such as carbon black, graphite, tin oxide and other metal oxides. "GC
The dielectric constant of S ′ ″ phenolic resin is reported to be 33. These parameters are related to the time constant by Equation 1.

[0021]

T _d = ε _o K _d / σ _d where t _d = time constant of donor roller (sec) ε _o = free space permittivity = 0.885 × 10 ⁻¹⁴ sec / (cm-ohm) K _d = dielectric constant of phenol resin coating (no unit) σ _d = conductivity of phenol resin coating (1 / (cm-ohm))

As can be seen from the above description, the physical property of the phenolic resin that can be most easily controlled to obtain the desired time constant is the electrical conductivity of the phenolic resin, which is the proper selection and concentration of additives. Can be controlled by. When the donor roller of the present invention is applied to hybrid scavengeless development using a magnetic brush transport roller, the most desirable range of this time constant is 1 to 300 microseconds, and the more desirable range is 30 to 70 microseconds.
Calculated to be microseconds.

The desired optimum discharge time constant in this range is substantially different from the previously preferred range in the scavengeless system, especially when using anodized aluminum donor rollers. For example, in the case of US Pat. No. 5,063,875 assigned to the assignee of the present invention, the surface conductivity of a suitable anodized aluminum donor roller is 1.
It is 0 ^-11 (ohm-cm) ^-1 . Anodized aluminum K
Considering that _d is 9, the resulting t
_{The d} is 80 microseconds, which is long compared to the dwell time at the nip between the donor and the photoreceptor and at the interface between the magnetic brush and the donor roller. For phenolic resin donor rollers having discharge time constants within the preferred range according to the present invention, a suitable range of conductivity is from 10 ^-8 to 1.
It is 0 ^-6 (ohm-cm) ^-1 .

Although the above-described embodiments provide many advantages in a practical development system, the preferred range for that particular physical property is selected by many, often competing, design parameters. These design constraints are due to the toner “loading” on the donor roller by the magnetic brush on the transport roller
This is especially clear in the case of the above mentioned hybrids. Among these design constraints are the surface charge relaxation (or discharge time constant) of the donor roller and the ability of the magnetic brush to deliver the maximum amount of toner to the donor roller through the nip between the magnetic brush and the donor roller. Related to the magnetic brush development relaxation as a function of the ability of the electric field between the transport roller and the donor roller, whose surface collapses rapidly upon leaving the nip, and the conductivity or insulation of the donor roller to the AC of the electrode wire. A, which affects the strength of the electric field near the wire
In order to equalize the C frequency relaxation and the strength of the electric field between the donor roller and the photoreceptor, the dielectric charge (di
electric charge) includes the image development response of the photoreceptor, which is generally believed to have to be able to relax at a faster rate than the image voltage of the photoreceptor can change.

Taking all of these constraints and others into account, particular ones of these constraints are, among other things, the thickness S _d of the dielectric layer forming outer surface 42 and its real dielectric constant K _d.
, The material of the outer surface 42 of the donor roller 41 can be filled by appropriate selection. In the actual application of scavengeless development, one or more of these constraints may be provided by providing the ratio of the dielectric layer thickness to the dielectric constant, S _d / K _d , within a certain range.
It can be easily satisfied (the unit of the ratio is expressed as length, since the dielectric constant has no unit). Some of the above design constraints that are met using this ratio can be summarized as follows.

S _d / K _d << electrode wire diameter (up to 50 μ
If m), the AC frequency relaxation conductivity constraint can be ignored. If S _d / K _d << is the gap between the donor roller and the photoreceptor (~ 300 μm), the constraint on the image development response of the photoreceptor can be ignored. If S _d / K _d << toner particle size (-10 μm), the magnetic brush development relaxation requirement can be ignored.

[Brief description of drawings]

FIG. 1 is a simplified front view of a hybrid scavengeless developing station incorporating a donor roller according to the present invention.

FIG. 2 is a simplified front view of a one-component scavengeless developing station incorporating a donor roller according to the present invention.

[Explanation of symbols]

 10 Photoconductive Belt 38 Housing 40 Donor Roller 41 Electrode Wire 42 Outer Surface 46 Conveying Roller 47 Developer Material 50 Sleeve 76 DC Power Supply 78 DC Voltage Power Supply 80 AC Voltage Power Supply 84 AC Voltage Power Supply

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Gerald Tee. Rioy Webster Heartsville Lane, NY 292 (72) Inventor Grace Tee. Blue Wington New York, USA Fairport Pioneer Drive 22 (72) Inventor Joseph G. Shulm United States New York, NY Liverpool Parker Avenue 124 (72) Inventor William H.C. Wayman United States New York, Ontario Lake Road 1945

Claims (7)

[Claims] 1. An apparatus for developing an electrostatic latent image, the apparatus having a housing defining a chamber for storing replenishment developer material therein, and an outer surface of a phenolic resin, at least partially A donor roller mounted in the chamber of the housing and configured to convey the developer material to the latent image; and an electrode member disposed in a proximity position from the donor roller in the space between the latent image and the donor roller. There is an electrical bias to separate the toner particles from the donor roller to form a toner powder cloud in the space between the electrode member and the latent image and to develop the latent image with the toner particles separated from the toner cloud. And an electrostatic latent image developing device. 2. The discharge time constant of the surface of the donor roller is 3
2. It is less than 00 microseconds.
The electrostatic latent image developing device described. 3. The electrostatic latent image developing device according to claim 1, wherein the phenol resin of the donor roller is doped until a conductivity of more than 10 ^-8 (ohm-cm) ^-1 is obtained. 4. An apparatus for developing an electrostatic latent image, the apparatus comprising a housing defining a chamber for storing replenishment developer material therein, and at least partially mounted within the chamber of the housing, An electrostatic latent image developing device comprising: a donor roller configured to convey a developer material to a latent image; and a discharge time constant of a surface of the donor roller is less than 300 microseconds. 5. An apparatus for developing an electrostatic latent image on a charge retentive surface, the apparatus comprising a housing having a chamber formed therein for storing replenishment developer material, and at least partially within a chamber of the housing. A donor roller configured to carry the developer material to the latent image, the outer layer having a conductive interior and a substantially non-metallic outer layer divided by its dielectric constant. An electrostatic latent image developing device having a thickness smaller than a distance between the donor roller and the charge holding surface. 6. An electrostatic latent image according to claim 5, wherein the thickness of the outer layer divided by its dielectric constant is smaller than the average diameter of particles of the developer material applied to the charge retentive surface. Development device. 7. An electrode member comprising at least one wire located in the space between the latent image and the donor roller and located at a close distance from the donor roller for separating toner particles from the donor roller. An electrically biased electrode member for forming a toner powder cloud in the space between the roller and the charge retentive surface and developing the latent image with toner particles separated from the toner cloud, the dielectric constant of which is 6. The electrostatic latent image developing device according to claim 5, wherein the thickness of the outer layer divided by is smaller than the diameter of the wire.